Overlap map for compositing needs to consider clipping

[Adrienne Walker]

The overlap map in RenderLayerCompositor currently doesn't consider clipping.  So, if there is a large layer that is clipped, it may cause other layers to unnecessarily become composited, even though they aren't truly overlapping once clip is considered.

See: http://crbug.com/85438

[Simon Fraser (smfr)]

I can haz testcase?

[Adrienne Walker]

Created attachment 98815 [details]
Test case

Here's a test case.  I have a patch too, but it changes the expected output from limit-layer-bounds-clipping-ancestor, so I need to clean that up first.

[Adrienne Walker]

Created attachment 98830 [details]
Patch

[Adrienne Walker]

(In reply to comment #3)
> Created an attachment (id=98830) [details]
> Patch

smfr: ping?

[Simon Fraser (smfr)]

Comment on attachment 98830 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=98830&action=review

> Source/WebCore/rendering/RenderLayerCompositor.cpp:569
> +    IntRect clipRect = layer->backgroundClipRect(rootRenderLayer(), true);

This is another walk up the layer tree, sadly.

[James Robinson]

That one should hit cache (saved m_clipRects on the parent layer) most of the time, at least.

[Simon Fraser (smfr)]

(In reply to comment #6)
> That one should hit cache (saved m_clipRects on the parent layer) most of the time, at least.

No, temporaryClipRects = true.

[Adrienne Walker]

Committed r91114: <http://trac.webkit.org/changeset/91114>

[Simon Fraser (smfr)]

The perf hit from this was significant: bug 84410